GLES2Dbg: organize calls into frames and contexts

Maintain a current state for each context updated by each call.
eglSwapBuffers Begins a new frame; clone current state.
Use clone to compute context for a call within that frame later on,
 in the context tree view.

Change-Id: I66658561f610025b203a991b5b9f545a9a2f9cd4
Signed-off-by: David Li <davidxli@google.com>
8 files changed